Method of deinking waste paper using cellulase without lowering paper strength and method of evaluating the same

ABSTRACT

A deinking method using a cellulase which enables the load upon the environment to be reduced; and an evaluation method whereby a cellulase effective in deinking and the effective addition level of the cellulase can be appropriately determined. 
     By proposing pulp-swelling activity (PSA) that elevates the water-retention value of pulp after pulp is reacted with cellulase, it becomes possible to select an enzyme that is effective in cellulase-deinking treatment without lowering the paper strength and to determine the effective enzyme dosage. Namely, a method of deinking waste paper is provided wherein the selection of an effective cellulase and the optimization of the enzyme dosage with the use of PSA as an indication make it possible to minimize the cellulase addition level and lessen the amount of the deinking agent.

TECHNICAL FIELD

The present invention relates to a method of deinking waste paper that lessens the load on the environment. The invention further relates to a method that evaluates cellulase that is effective in deinking whereby the paper strength (intensity) is not reduced and a usage amount of deinking agents is lowered, and an effective dosage of the cellulase.

BACKGROUND ART

Deforestation is cited as a cause of global warming and the reduction of carbon-dioxide emissions is the focus of attention as a global environmental problem. Forest resources are utilized in contemporary industries in the forms of wood, pulp, and paper. Various methods are being studied to reduce the amount of deforestation in order to prevent global warming. In the field of paper, efforts are being made worldwide to increase the rate of waste paper recycling.

Waste paper deinking is largely established as a method of waste paper recycling. In current methods, alkalis such as sodium hydroxide and sodium silicate, oxidative bleaching agents such as hydrogen peroxide, chelating agents, and agents such as surfactants are added to the waste paper to accelerate the release of ink from the pulp fiber. Thereafter, a washing technique and/or flotation technique is used to carry out deinking to separate the pulp and ink.

However, due to the variety of raw materials used in waste paper and the variety of printing techniques, deinking by the conventional deinking techniques is becoming problematic. Further, in order to solve problems concerning adhesion of foreign matter (stickies), fiber damage, effluent load and the like, neutral deinking is attracting attention as a deinking method that is kinder to the environment. In order to carry out neutral deinking more effectively, enzymatic treatments utilizing cellulase and the like are being studied.

A number of proposals have been put forth concerning deinking methods for waste paper using cellulase derived from fungi or bacteria. Kao Corp. proposes a deinking agent containing cellulase in JP Patent Publication (Unexamined Application) No. 59-9299, however there is no disclosure therein regarding the putative lowering of paper strength due to the action of the cellulase. In JP Patent Publication (Examined Application) No. 3-57235, Honshu Paper Co., Ltd. proposes a deinking technique for waste paper in which enzymatic treatment using alkali-resistant cellulase is performed at the same time as treatment with an alkaline deinking agent or after treatment with the deinking agent. In Japanese Patent No. 2805313, Oji Paper Co., Ltd. discloses a deinking technique in which treatment is conducted with a deinking agent after enzymatic treatment that contains cellulase. Further, in Japanese Patent No. 3042718, Novo Nordisk A/S attempts to find an enzyme component that can perform effective deinking by producing monocomponent cellulase. However, none of the above methods succeeded in providing an effective means for selecting an enzyme that realizes, at a low cost, a deinking effect that reduces the amount of the chemical agents that constitute an environmental burden or lower the strength (intensity) of waste paper in deinking.

Although various studies are being conducted, the rate of diffusion of enzymatic deinking is extremely low. Up to now, studies have been conducted on the application of cellulases to areas such as elimination of vessel pick, improvement of paper machine runnability and drainage, and deinking of waste paper. However, because of the high cost of cellulases and the fact that the action and effects of cellulases is not clear, the current situation is that cellulase has not been offered for practical use in areas other than elimination of vessel pick. Furthermore, because cellulase is an enzyme that degrades cellulose fiber, it has been pointed out that a decrease in the yield and the strength (intensity) of waste paper pulp after deinking is prone to occur.

Meanwhile, in deinking of waste paper, because the objects of effective deinking involve detachment and saponification of printing ink and pulp swelling, alkaline chemical agents and the like are used that amount to as much as several percent of the dry pulp weight. Further, as pulp is normally treated by being suspended in water of a volume that is equivalent to several dozen times the weight of the dry pulp, a vast amount of alkaline effluent is generated. Thus, because chemical agents are used in the treatment to neutralize the effluent, the recovery treatment is one that involves a heavy environmental burden. There is a need for development of an environmentally friendly deinking method that improves the current deinking technology that creates a heavy environmental burden.

Waste paper recycling is technology that indirectly protects forest resources and contributes to conservation of the global environment. It is anticipated that by further improvements such as reducing the environmental burden caused by waste effluent and decreasing the usage amount of chemical agents, the environmental adaptability of waste paper recycling will be enhanced. Thus, it was expected that enzymatic deinking would be applied as a technique to effectively remove ink at a neutral pH. However, its application has been postponed due to problems concerning decreases in the strength (intensity) of waste paper pulp and the cost of enzymes. Accordingly, the object of the present invention is to provide a cellulase deinking method for waste paper without lowering paper strength, that is implemented using an economically feasible enzyme amount that reduces the amount of deinking agents.

DISCLOSURE OF THE INVENTION

As described above, in waste paper deinking using cellulase, it is desirable that the deinking effect be obtained using a cost-effective amount of enzyme without lowering the paper strength (intensity). Therefore, we tested a fraction of each cellulase component of cellulases derived from fungi, and evaluated the activity of the obtained enzyme components towards pulp, the waste paper deinking action, and the intensity characteristics of the enzyme-treated waste paper.

Surprisingly, we found that by allowing an extremely small level of cellulase components comprising a marked amount of endoglucanase to act on pulp, the conventionally known action of cellulase of degrading cellulose to yield cellulose degradation products such as glucose hardly occurred, and the degree of swelling, which is indicated by the water retention value of the pulp, increased. Specifically, we found that the cellulose fiber constituting the pulp was hydrated to cause the pulp to swell. Conventionally, pulp swelling is an effect that has been found in sodium hydroxide and liquid ammonia, which are alkaline chemical agents, however this phenomenon had not been found with regard to cellulase.

As a result of further concentrated studies, we found that, with regard to pulp swelling and waste paper deinking effects produced by cellulase, a favorable correlation exists in the kinds of cellulase effective in waste paper deinking and the kinds of cellulase having a swelling action. As a result, we found that, surprisingly, fungi-derived endoglucanase expresses waste paper deinking activity in a dosage level that is lower than the enzyme dosage used in treatment reported up to now, and also that the intensity of waste paper that underwent enzymatic deinking compared favorably to the intensity of the waste paper prior to the enzymatic treatment. Further, when we compared deinking activity exerted by endoglucanase with that of sodium hydroxide, sodium silicate, and hydrogen peroxide, which are deinking agents that are currently in widespread use, we found that cellulase reduces the usage amount of these chemicals, or exhibits an effect that adequately substitutes for these chemicals. Thus we succeeded in completing the present invention.

Namely, by evaluating pulp-swelling activity (PSA) that is determined by measuring an increase in the water retention value of pulp according to the present invention, it is possible to determine an effective enzyme and an effective enzyme usage level for a target waste paper deinking application.

The present invention relates to a method of deinking waste paper characterized by the use of cellulase that exhibits pulp-swelling activity (PSA). The present invention further relates to: a method characterized by being conducted with cellulase of a dosage level wherein pulp-swelling activity (PSA) is 25 units (25 U) or more; a method characterized by being conducted with cellulase of a dosage level wherein pulp-swelling activity (PSA) exhibits a maximum value; a method wherein the cellulase is endoglucanase; and the above method wherein endoglucanase is SCE3 derived from Trichoderma genus, NCE4 derived from Humicola genus, or RCEI derived from Rhizopus genus.

The present invention also relates to an evaluation method for obtaining a cellulase enzyme and an enzyme dosage that are effective in deinking of waste paper without lowering the paper strength. The present invention further relates to: an evaluation method characterized by measuring the degree of swelling of pulp after reacting cellulase with pulp; an evaluation method characterized by measuring a change in the water retention value (WRV) of pulp after reacting pulp with cellulase for 60 min at the optimal pH and optimal temperature of the enzyme used at a pulp consistency of 1% (w/v); and to an evaluation method characterized by determining pulp-swelling activity (PSA), wherein cellulase activity that increases the water retention value (WRV) of pulp by 1% is taken as 10 units (10 U) after reacting cellulase for 60 min under conditions of a pulp consistency of 1% (w/v), optimal pH, and optimal temperature, employing 0.5 g of oven-dried pulp as a substrate.

Cellulase used in the present invention is characterized by containing endoglucanase. More specifically, cellulase containing monocomponent endoglucanase or specific endoglucanase components in a large amount or the like can be used, but a method of manufacturing the enzyme preparation is not limited. Further, the origin of endoglucanase contained in the cellulase may be any organism that produces endoglucanase, such as fungi (Trichoderma genus, for example T. reesei or T. viride; Humicola genus, for example H. insolens; Acremonium genus, for example A. cellulolyticus; Rhizopus genus, for example R. oryzae; Mucor genus, for example M. circinelloides; Phycomyces genus, for example P. nitens; and the like) or bacteria (Bacillus genus, Pseudomonas genus, Clostridium genus, and the like) or the like. Further, an enzyme derived from a transformant in which a gene of the above endoglucanases is introduced can be used, and the origin is not limited by the present description.

Cellulase is an enzyme that degrades a water-insoluble cellulose substrate by the synergistic action of a number of kinds of enzyme, and β-glucosidase, endoglucanase, and cellobiohydrolase are known components thereof. For example, known components of endoglucanase derived from Trichoderma genus include EG I to EG IV, and known components of endoglucanase derived from Humicola genus include EG I to EG V, and all of these can be utilized in the method of the present invention. Further, each component of cellulase may be classified into a sugar hydrolase family as proposed by Hennrissat et al. In recent years, it has become known that families in which endoglucanase (EC.3.2.1.4) is present include 5, 6, 7, 8, 9, 12, 44, 45, 48, 51, 61, 74 and the like. For example, it is known that endoglucanase II derived from Trichoderma viride is classified into family 5, and endoglucanase V derived from Humicola insolens is classified into family 45.

Commercially available cellulase is mainly produced as a mixture of the above three components by a microorganism such as bacteria or fungi. By devising the conventional culture conditions it has been possible to somewhat alter the composition ratio of enzyme components, but imparting a major alteration has proved difficult. However, because the selection and expression of a specified gene has become possible as a result of progress in genetic engineering techniques in recent years, the possibility has increased of being able to isolate and identify a specific cellulase component effective in treatment of paper pulp and, furthermore, to manufacture a highly expressing clone to create a novel enzyme that offers excellent cost efficiency.

The present inventors already provide cellulase derived from Trichoderma genus, cellulase derived from Humicola genus, cellulase derived from Rhizopus genus, and the like, as the above kind of cellulase derived from fungi. Similar cellulases are also provided by Genencor mt. Inc., Novo Nordisk A/S, logen Corp., and the like. Meanwhile, KAO Corp. provides Bacillus genus cellulase as cellulase derived from bacteria. In the present invention, it is also possible to use these cellulases. Preferable examples to be used herein include SCE3 (SEQ ID NO:3 and SEQ ID NO:4), which is endoglucanase derived from Trichoderma genus, NCE4 (SEQ ID NO:5 and SEQ ID NO:6), which is endoglucanase derived from Humicola genus, RCE1 (SEQ ID NO:1 and SEQ ID NO:2), which is endoglucanase derived from Rhizopus genus, and the like, which are already provided by the present inventors.

In the present invention, as endoglucanase we selected SCE3 disclosed in WO 98/54332 as cellulase derived from Trichoderma genus and NCE4 disclosed in WO 98/03640 as cellulase derived from Humicola genus, and conducted a comparison of the deinking activity by means of the following experiments.

Method for Determining Pulp-swelling Activity (PSA)

The pulp-swelling activity (PSA) as proposed by the present invention was determined in the following manner. 0.5 g of oven-dried pulp that was disintegrated for 20 min by a standard disintegrator as described in JIS (Japanese Industrial Standard) P-8209 was suspended in a buffer solution having the optimal pH for the enzyme to be used in evaluation to bring the pulp consistency to 1% (w/v), and the enzyme was then added thereto and reacted at the optimal temperature for 60 min. To measure the degree of swelling of the pulp after reaction, the water retention value (WRV), which is one indicator of the degree of swelling, was measured according to the water retention value (WRV) measurement method for pulp described on p. 73 of “KAMI PARUPU NO SHIKENHOU (A method for testing paper pulp)” (edited and published by The Japan Technical Association of the Pulp and Paper Industry, 1995). The degree of swelling (water retention value) was also measured for untreated pulp in the same way. The water retention value of the pulp treated with enzyme was compared with the water retention value of the untreated pulp, and enzyme activity that increased the water retention value by 1% was taken as 10 units (10 U), and the unit was defined as pulp-swelling activity (PSA).

The pulp-swelling activity (PSA) is not necessarily proportional to the added level of enzyme, however, when the level of added enzyme is too small PSA decreases as the pulp does not swell, and when the level of added enzyme is too large PSA decreases because the cellulose fibers of the pulp are excessively cut and water cannot be contained among the fibers. Therefore, PSA exhibits a peak (maximum value) at an enzyme dosage within a certain range.

Because the deinking effect is enhanced as pulp-swelling activity (PSA) increases, a preferable enzyme for carrying out the present invention is an enzyme that exhibits a higher numerical value for PSA even when the added level of the enzyme is small. Specifically, a preferable enzyme is one exhibiting a pulp-swelling activity (PSA) value of 25 units (25 U) or more per 0.5 g of oven-dried pulp. Further, when the added amount of enzyme used exhibits a pulp-swelling activity (PSA) value of 25 units (25 U) or more, as previously described, it is preferable that the PSA value is in the vicinity of its maximum, and the range thereof suitably changes according to the enzyme used.

In the present invention, the optimal pH and optimal temperature of an enzyme can be determined by the following procedure. Buffer solutions used herein in determining the optimal pH are as follows: for pH 4 to 5.5, a 50 mM acetate buffer; for pH 6 to 8, a 50 mM phosphate buffer; and for pH 9, a 50 mM glycine-sodium hydroxide buffer.

0.5 ml of solution containing enzyme is added to 0.5 ml of buffer solution containing 2% of CMC (carboxymethylcellulose, manufactured by Tokyo Kasei Kogyo Co., Ltd.) dissolved therein, and the mixture is then incubated at 30 to 70° C. for 30 min. Subsequently, the concentration of reducing sugar produced in the obtained reaction solution is determined by a 3,5-dinitrosalicylic acid method (DNS method). More specifically, 3.0 ml of DNS reagent is added to 1.0 ml of reaction solution 30 min. after reaction, the mixture is incubated for 5 min in a boiling water bath, diluted with 8.0 ml of distilled water, and the absorbancy at 540 nm is then determined. A calibration curve is then created using glucose solution diluted in a stepwise manner, and the amount of reducing sugar produced in the enzyme reaction solution is determined using glucose conversion. Activity is calculated by taking as 1 unit an enzyme level that produces reducing sugar corresponding to 1 μmol of glucose in 1 min. The DNS reagent can be prepared in accordance with descriptions in the literature (for example, “SEIBUTSU KAGAKU JIKKENHOU 1—KANGENTOU NO TEIRYOUHOU (Biochemical experimental method 1—Quantitative method of reducing sugar)” p. 19-20, 1981, Fukui Sakuzou, GAKKAI SHUPPAN CENTER).

Deinking Activity of Cellulase

The deinking activity of cellulase was determined as described below when using waste newspaper cut into 3 cm-square pieces as the raw material waste paper. Waste paper pulp was obtained by disintegrating 24 g of oven-dried raw material waste paper at 50° C. for 20 min using a standard disintegrator as described in JIS P-8209. Cellulase was added to the waste paper pulp for which the pH was adjusted by buffer solution or sulfuric acid, and enzyme reaction was conducted for 1 hour at 50° C. After the reaction, distilled water at 50° C. was added to the waste paper pulp to bring to 4.5 L, the mixture was provided to an experimental flotator (FW model flotation test apparatus, manufactured by KYOUSIN SANGYOU CO., LTD.), a deinking agent (Lipotol LH-350, manufactured by NIKKA Chemical Co., Ltd.) of 0.1 to 0.5% (w/v) of the oven-dried pulp was added thereto, and flotation was conducted for 10 min. The pulp was then recovered, washed with distilled water and dehydrated, diluted with distilled water to bring to a pulp consistency of 0.15% (w/v), and made into paper using a handsheets machine according to a method described in JIS P-8209 to obtain a hand-made paper. For comparison, the same procedure was performed on waste paper pulp that was not treated with cellulase to obtain a sample untreated with cellulase. The brightness of the hand-made paper was determined using a reflectance measuring instrument in accordance with JIS P-8123. Measurement was similarly performed for the sample untreated with cellulase and the value obtained by subtracting the brightness of the sample untreated with cellulase from the brightness of the cellulase treated sample was defined as A brightness (deinking activity).

When the deinking activity of individual components of cellulase is compared, although superior deinking activity can not be found for cellobiohydrolase, which is considered to promote degradation from the terminus of cellulose, at an added enzyme level in the range of 0.001 to 0.1% (w/w) with respect to oven-dried pulp. However, for endoglucanase, which is considered to randomly degrade the cellulose chain, deinking activity can be found at the low added enzyme level of 0.01% (w/w) or less. Further, when enzymatic treatment is carried out at an excessive level such as 0.1% (w/w), the deinking effect declines.

In the method of waste paper deinking using cellulase, the added level of cellulase is shown by the cellulase activity or the cellulase weight with respect to the weight of normal dry pulp. Regarding the added amount of cellulase, any amount can be added as long as it is within the range of amounts that can exert a deinking effect. However, normally the minimum amount adequate for exhibiting effective deinking activity is added due to cost considerations. When an enzyme dosage that can exert a deinking effect is represented by the pulp-swelling activity (PSA) proposed herein, it can be defined as a cellulase dosage that exhibits activity of 25 U or more with respect to 0.5 g of oven-dried pulp. Further, regarding the level of added cellulase, when representing enzyme activity using hydroxymethyl cellulose (HEC) as a substrate, if an enzyme amount that reduces 1 nmol of substrate with respect to 1 g of oven-dried pulp is defined as 1 nkat/g pulp, a cellulase amount within the range of 0.01 nkat/g pulp to 10000 nkat/g pulp can be added. Preferably, an added level is 100 nkat/g pulp or less, and more preferably 10 nkat/g pulp or less.

In the common deinking processes, after suspending waste paper in water and disintegrating it using a disintegrating apparatus such as a pulper, deinking agents such as sodium hydroxide, sodium silicate, hydrogen peroxide or chelating agents are added thereto and aging is performed. The waste paper is then deinked by subjecting it to flotation or washing it together with a deinking agent that is a surfactant to remove printing ink. Preferably, the cellulase treatment according to the method of waste paper deinking provided by the present invention is employed at the same time as the disintegration step or at the time of aging after the disintegration step instead of the conventionally used deinking agents. At that time, in order to exert cellulase activity at its maximum, the pH can be adjusted using a quantity of acid or alkali, such as sulfuric acid or sodium hydroxide, such that the waste paper pulp is maintained at the optimal pH of the cellulase, and addition of a buffer solution is also possible.

Waste paper subjected to cellulase deinking may be any normally used waste paper, and preferable examples thereof include waste newspaper, magazine waste paper, office waste paper, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in further detail by means of examples. However, the examples are not intended to limit the scope of the present invention.

EXAMPLE 1 Determination of Pulp-swelling Activity (PSA) of Trichoderma Genus-derived Endoglucanase II (EGII) and Cellobiohydrolase I (CBHI)

0.5 g of oven-dried waste newspaper that was disintegrated for 20 min using a standard disintegrator (TAPPI Pulp Disintegrator, manufactured by Toyo Seiki Seisaku-sho, Ltd.) was suspended in a 50 mM citrate buffer solution (pH 5) to bring the pulp consistency to 1% (w/v). Purified EGII or purified CBHI prepared from commercially available Meicelase TP 60 (Meiji Seika Kaisha, Ltd.) based on the method of Rahkamo, L. et al. (Cellulose, 3, 153-163 (1996)) was then added thereto at 0.02% (w/w) with respect to the oven-dried pulp. After reaction at 50° C. for 60 min, the degree of pulp swelling was determined based on the method for measuring the water retention value (WRV) of pulp described on p. 73 of “KAMI PARUPU NO SHIKENHOU (A method for testing paper pulp)” (edited and published by The Japan Technical Association of the Pulp and Paper Industry, 1995). Pulp-swelling activity (PSA) was determined by comparing the water retention value of pulp treated with enzyme with the water retention value of untreated pulp, and taking enzyme activity that increased the water retention value by 1% as 10 units (10 U). The results are shown in Table 1. The results in Table 1 show that under the above reaction conditions, although cellobiohydrolase exhibits no pulp-swelling action, endoglucanase exhibits a pulp-swelling action that increases the water retention value of pulp.

TABLE 1 Enzyme PSA [U] Untreated — EGII 35 CBHI  0

EXAMPLE 2 Deinking Test

Twenty-four grams of oven-dried waste newspaper cut into 3 cm-square pieces was disintegrated using a standard disintegrator as described in JIS P-8209 (TAPPI Pulp Disintegrator, manufactured by Toyo Seiki Seisaku-sho, Ltd.) at 50° C. for 20 min. The obtained waste paper pulp was adjusted to pH 5 with a 50 mM citrate buffer solution, and cellulase was then added thereto to bring to respective dosage of 0.001, 0.01, and 0.1% (w/w) with respect to the oven-dried pulp, and enzyme reaction was conducted for 1 hour at 50° C. The cellulases used were CBHI, i.e., cellobiohydrolase, and SCE3 (described in WO 98/54332), in which the endoglucanase component is enhanced, of Trichoderma genus, for which the optimal pH is in the vicinity of pH 5; and NCE2 (described in JP Patent Publication (Unexamined Application) No. 8-126492), in which cellobiohydrolase is enhanced, and NCE4 (described in WO 98/03640), in which the endoglucanase component is enhanced, of Humicola genus, for which the optimal pH is in the vicinity of pH 6. After reaction, distilled water at 50° C. was added to the waste paper pulp to bring to 4.5 L, the mixture was then provided to an experimental flotator (FW model flotation test apparatus, manufactured by KYOUSIN SANGYOU CO., LTD.), and a deinking agent (Lipotol LH-350, manufactured by NICCA Chemical Co., Ltd.) of 0.3% (w/v) of the oven-dried pulp was added thereto, and flotation was conducted for 10 min. Thereafter, the pulp was recovered using a 140 mesh sieve, washed with distilled water and dehydrated. It was then diluted with distilled water to bring to a pulp consistency of 0.15% (w/v), and a hand-made paper was then prepared using a handsheets machine by the method described in JIS P-8209. For comparison, the same procedure was performed on waste paper pulp that was not treated with cellulase to obtain a sample untreated with cellulase. The brightness of the hand-made paper was determined using a reflectance measuring instrument (spectrophotometer CM5251, manufactured by Minolta) in accordance with JIS P-8123. The difference between the brightness of the cellulase treated sample and the brightness of the sample untreated with cellulase was defined as Δ brightness. Further, the PSA was determined in the same manner as in Example 1. The tensile strength and tear strength were determined in accordance with JIS P-8113 and JIS P-8116, respectively, and the tensile index and tear index were calculated.

Tables 2 and 3 show the results of measurement of the deinking effect of cellobiohydrolase and endoglucanase of Trichoderma genus and Humicola genus. The results in Table 2 show that no deinking effect was observed for cellobiohydrolase which does not have a swelling action. Further, the results of Table 3 showed that, in the low dosage level of 0.01% (w/w) or less of oven-dried pulp weight in which PSA is 25 U or more, endoglucanase having a pulp swelling action has a deinking effect without causing a significant decrease in intensity. In addition, it was found that when enzymatic treatment is conducted at the excessive level of 0.1% (w/w), the deinking effect is decreased or the intensity declines. Furthermore, when we analyzed the intensity of waste paper treated with endoglucanase of the low dosage of 0.01% (w/w) of oven-dried pulp weight in which PSA is 25 U or more, an action of cellulase that lowers the paper strength that was observed in the conventional cellulase deinking treatment (0.1% treatment in Table 3) was hardly observed, indicating that the negative effect regarding intensity caused by cellulase treatment had been overcome.

TABLE 2 Enzyme/added Δ PSA level Brightness Brightness [U] Untreated (pH 5) 43.3 — — CBHI/0.001% 43.1 −0.2 0 CBHI/0.01% 43.2 −0.1 0 CBHI/0.1% 42.7 −0.6 0 Untreated (pH 6) 43.5 — — NCE2/0.001% 42.2 −1.3 0 NCE2/0.01% 43.4 −0.1 0 NCE2/0.1% 43.5 0 0

TABLE 3 Tensile Enzyme/added Δ PSA index Tear index level Brightness Brightness [U] [NM/g] [mNm2/g] Untreated (pH 5) 43.3 — — 27.5 6.4 SCE3/0.001% 44.0 0.7 29 28.2 6.4 SCE3/0.01% 47.0 3.7 97 26.3 6.0 SCE3/0.1% 45.0 1.7 19 23.8 4.2 Untreated (pH 6) 43.5 — — 27.8 6.2 NCE4/0.001% 46.0 2.5 32 28.2 6.2 NCE4/0.01% 44.7 1.2 56 28.4 6.1 NCE4/0.1% 44.6 1.1  8 25.2 5.8

EXAMPLE 3 Comparison of Conventional Chemical Deinking and Enzymatic Deinking

We investigated the effect of enzymatic deinking with regard to lowering the usage amount of chemical deinking agents, taking the standard usage amount of conventionally used deinking agents to be 1.5% (w/w) sodium hydroxide+3% (w/w) sodium silicate+0.5% (w/w) hydrogen peroxide with respect to oven-dried pulp. In the same manner as in Example 2, waste paper pulp subjected to enzymatic treatment with SCE3 of 0.01% (w/w) was treated with deinking agents of usage amounts graded in three steps, i.e., the usage amounts were ¼, ½, and the equivalent of the above standard usage amount, respectively. Treatment with the agents was performed by immersing the waste paper pulp in the agents for 60 min at 50° C. Thereafter, the brightness was determined in the same manner as in Example 2. The results are shown in Table 4. The Δ brightness of untreated+agents (section of experiment with no enzymatic treatment and use of the standard amount of deinking agents) and the Δ brightness of SCE3+½ agents (section of experiment with a step of treatment with SCE3 of 0.01% and use of ½ the standard amount of deinking agents) were roughly equal. Thus, it was found that use of cellulase treatment in deinking treatment makes it possible to decrease the usage amount of deinking agents by approximately ½.

TABLE 4 Δ Treatment condition Brightness Brightness Untreated 43.5 — Untreated + agents 49.1 5.6 SCE3 44.7 1.2 SCE3 + ¼ agents 45.0 1.5 SCE3 + ½ agents 48.6 5.1 SCE3 + agents 51.1 7.6

INDUSTRIAL APPLICABILITY

The present invention enables the evaluation and selection of cellulase having effective pulp swelling activity in waste paper deinking, and provides a low cost method of deinking waste paper that is kind to the environment in which the amount of deinking agents used is reduced without lowering paper strength, using an enzyme dosage that is lower than the dosage used conventionally.

All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety. Also, it will be readily understood by a person skilled in the art that miscellaneous variations and modifications of the present invention are possible without deviating from the technical ideas and scope of the invention as disclosed in the attached claims. The present invention is also intended to encompass such variations and modifications. 

1. A deinking method for waste paper without lowering paper strength comprising treating waste paper with endoglucanase, wherein: (a) the endoglucanase is used at 0.01 % (w/w) or less with respect to oven-dried pulp; and (b) the endoglucanase is used at a dosage exhibiting a pulp-swelling activity (PSA) which is 25 units (25 U) or more.
 2. The method of claim 1, in which the endoglucanase is SCE3 derived from Trichoderma genus, NCE4 derived from Humicola genus, or RCEI derived from Rhizopus genus. 